1. Field of the Invention
The present invention relates to a coordinate input apparatus and method.
2. Description of the Related Art
There exist coordinate input apparatuses configured to allow a user to input coordinates by pointing to a coordinate position on a coordinate input surface with a pointing tool or device (e.g., a dedicated input pen or a finger) so as to control a connected computer or to write characters or graphics.
Hitherto, such coordinate input apparatuses have been proposed or commercialized as touchscreens of various types.
There are various coordinate input methods using, for example, a resistive film or ultrasonic waves. For example, U.S. Pat. No. 4,507,557 discusses a coordinate input method using light.
U.S. Pat. No. 4,507,557 discusses the following configuration. A retroreflective sheet is provided outside a coordinate input region. Sets of an illuminating unit configured to illuminate the coordinate input region with light and a light receiving unit configured to receive light are provided at corner end portions of the coordinate input region. Then, an angle between a light-blocking object, such as a finger, and each of two light receiving units is detected. Thus, the position pointed to by the light-blocking object is determined based on results of the detection.
U.S. Pat. Nos. 6,429,856 and 6,570,103 discuss coordinate input apparatuses configured to have a retroreflective member provided around the periphery of a coordinate input region and to detect coordinates of a portion that blocks retroreflected light (light-blocking portion).
In a coordinate input apparatus discussed in U.S. Pat. No. 6,429,856, waveform data represents the distribution of intensity of light output from a light receiving unit that receives retroreflected light. A peak in the waveform data, which corresponds to a light-blocking portion generated by a light-blocking object, is detected by performing a waveform processing operation, such as a differential operation, on the waveform data. Then, coordinates of the position of the light-blocking object are calculated from a result of the detection. Further, in a coordinate input apparatus discussed in U.S. Pat. No. 6,570,103, one end and the other end of a light-blocking object are detected by comparison between image data and a specific threshold level pattern. Then, the center of the coordinate positions of the one end and the other end of the light-blocking object is detected.
Hereinafter, a system for calculating coordinates by detecting a light-blocking position, as discussed in U.S. Pat. Nos. 4,507,557, 6,429,856, and 6,570,103, is referred to as a light-blocking system.
The above-described coordinate input apparatuses may cause the following problem. In a case where a position on a coordinate input surface is pointed to, a part of the operator's body other than a pointing tool, such as a finger or a pen, may touch the coordinate input surface. Thus, coordinates may be detected at a position different from a correct position to which the operator intends to point. Consequently, a malfunction may occur.
U.S. Pat. No. 6,480,187 discusses a technique for disabling, in a case where an operator's palm or elbow touches a coordinate input surface, a detected position, as a countermeasure against the above-described problem. More specifically, a range blocked by a pointing tool is measured. Then, the size of the pointing tool is calculated. Thus, the kind of the pointing tool is determined. In the case of coordinates of a position pointed to by an object that is not a predetermined pointing tool, those coordinates are not output.
International Publication No. WO/2005/031554 discusses an apparatus configured to calculate a coordinate position using two imaging units for capturing an image of a pointed shadow. In this apparatus, each of the imaging units includes an image sensor, a lens, and a light source. The light source is provided in the vicinity of one of the left and right sides, which is an upper side in the horizontal direction of the image sensor. The coordinate position of a pointing tool is calculated utilizing the coordinates of an upper end portion of an image of the shadow. With this configuration, only an end portion of a pointing tool, which is at the side closer to a detection unit provided at an upper part of a detection surface, is detected. Thus, the detection of a pointed coordinate position is not affected by an operator's palm, etc., which is located lower than the end portion of the pointing tool.
In addition, a coordinate input apparatus of the light-blocking system type capable of detecting a plurality of coordinate positions has been devised to allow a plurality of operators to simultaneously input coordinates.
Japanese Patent Application Laid-Open Nos. 2002-055770 and 2003-303046 and Japanese Patent Registration No. 2896183 discuss apparatuses configured to detect angles of a plurality of light-blocking portions using a single light receiving sensor, to calculate several input coordinate candidates from a combination of angles of sensors, and to determine coordinates actually input from the input coordinate candidates.
For example, in a case where two-point input is executed, coordinate positions of up to four points are calculated as input coordinate candidates. Among the four points, two points actually input by an operator are determined and output. That is, in this determination, actual input coordinates (corresponding to real images) and false input coordinates (corresponding to virtual images) are discriminated among a plurality of input coordinate candidates. Thus, final input coordinates are determined. Hereinafter, this determination is referred to as “real/virtual determination”.
Japanese Patent Application Laid-Open Nos. 2002-055770 and 2003-303046 discuss the following method as a more specific method for “real/virtual determination”. That is, first and second sensors are provided at both ends of one side of a conventional coordinate input region, respectively, by being spaced from each other a distance sufficient to calculate coordinates of a position pointed on the coordinate input region with good precision. In addition, a third sensor is provided at a position between the first sensor and the second sensor by being spaced therefrom a sufficient distance. Then, the “real/virtual determination” is performed on angle information representing a plurality of angles of a light-blocking portion detected by the first sensor and the second sensor based on angle information obtained by the third sensor, which differs from the angle information detected by the first sensor and the second sensor.
However, the conventional light-blocking system cannot always determine an operator's unintentional input due to the operator's palm or elbow or a sleeve of the operator's clothes as a false detection.
In a stationary state, it is often that the shadows of, for example, an operator's palm or elbow or a sleeve of the operator's clothes are larger than the shadow of a pointing tool (assumed to be a finger or a pointing pen). However, in a transient state in which the shadows of an operator's palm or elbow or a sleeve of the operator's clothes enter or exit the light-blocking region, sometimes, the shadow thereof formed by blocking light can be small and cannot always be larger than that of the pointing tool. That is, in a case where the width of a shadow to be determined as an erroneous input object is substantially equal to or smaller than that of the pointing tool, such a shadow cannot be determined as an erroneous input object. The technique discussed in U.S. Pat. No. 6,480,187 does not solve this problem.
Among a plurality of coordinate candidates, a true input coordinate position is not always located above an erroneous input coordinate position. This phenomenon is described below with reference to FIGS. 12A and 12B.
FIG. 12A illustrates a case where a true input coordinate position 1284 and an erroneous input coordinate position 1282 are vertically arranged on a coordinate input region 2800. Neither a position 1281 nor a position 1283 is actually pointed to. However, the coordinates of the positions 1281 and 1283 are those of virtual images, which are calculated as coordinate candidates. In this case, the true input coordinate position 1284 is located above the erroneous input coordinate position 1282. Thus, even a conventional apparatus can determine the erroneous input coordinate position 1282 as an erroneous input.
FIG. 12B illustrates a case where a true input coordinate position 1285 and an erroneous input coordinate position 1287 are horizontally arranged on the coordinate input region 2800. Neither a position 1286 nor a position 1288 is actually pointed to. However, the coordinates of the positions 1286 and 1288 are those of virtual images, which are calculated as coordinate candidates. In this case, the true input coordinate 1285 is located lower than the erroneous input coordinate position 1287. Thus, a conventional apparatus cannot determine the erroneous input coordinate position 1287 as an erroneous input.
Thus, in a case where among the four coordinate candidates, a pair of coordinate positions including a true input coordinate position is arranged in a substantially horizontal direction, a coordinate position to be detected as an erroneous input coordinate position can be located upper than the true input coordinate position. The apparatus discussed in International Publication No. WO/2005/031554 selects an upper coordinate position as a true input coordinate position. Thus, the apparatus discussed in International Publication No. WO/2005/031554 does not solve this problem.
On the other hand, it is considered that a plurality of coordinate positions including that of a pointing tool and those of erroneous input objects due to an operator's palm or elbow or a sleeve of the operator's clothes are calculated using apparatuses discussed in Japanese Patent Application Laid-Open Nos. 2002-055770 and 2003-303046 and Japanese Patent Registration No. 2896183, which can detect a plurality of coordinate positions, and that an upper coordinate position is selected from among a plurality of coordinate candidates as that of the pointing tool.
However, even in this case, although the “real/virtual determination” for selecting a pair of real images due to a true input and an erroneous input from among a plurality of coordinate candidates can be performed as described above, it is difficult to determine which of the real images of the selected pair is the coordinate position due to a true input.